Gangliosides have been shown to inhibit mitogenesis by concanavalin A (Con A) and lipopolysaccharide (LPS) in murine spleen or thymus and by phytohemagglutinin and pokeweed mitogen in human peripheral blood lymphocytes. In this research, the cellular and biochemical mechanisms of ganglioside effects on mitogenesis will be studied, using Con A induction of T-cell mitogenesis and LPS induction of B-cell mitogenesis in murine spleen cell cultures. Preliminary results show that inhibition of LPS-induced mitogenesis by purified bovine brain ganglioside is independent of the presence of serum, whereas modulation of Con A-induced mitogenesis is serum dependent. These effects of exogenous ganglioside may be related to: (1)\direct inhibitory effects of gangliosides due to uptake of ganglioside into cells involved in the mitogenic response; (2)\indirect effects of gangliosides by interaction with interleukins required for mitogenesis; and (3)\synergism with endogenous serum gangliosides. The first possibility will be tested by determining the uptake of gangliosides in isolated spleen cell subpopulations and by studying ganglioside-altered cells with respect to their mitogenic response in reconstituted systems, synthesis of arachidonic acid metabolites that are known to alter mitogenesis and synthesis of DNA, RNA and protein. The second possibility will be tested in reference to preliminary results which show that gangliosides inhibit interleukin-2 (IL-2)-dependent CT6 cell growth. This effect will be explored further by studies of (1)\ganglioside effects on IL-2 activity from spleen cell cultures; (2)\ganglioside blocking of purified IL-2 binding; (3)\ability of gangliosides from CT6 cells and antibodies raised against these gangliosides to modulate IL-2 activity; and (4)\appearance of ganglioside at the cell surface of T cells undergoing blastogenesis. The general significance of endogenous ganglioside will be studied by assessing endogenous synthesis, release and re-uptake of glycolipid in lymphoid cells and the role of ganglioside in inhibition of mitogenesis by human serum lipoprotein. Also, a component of bovine brain gangliosides which stimulates B-cell proliferation will be further characterized. The results of this research should determine the significance of in vitro results to in situ immune responses and may lead in the direction of gangliosides as in vivo modulators of immune function.